Abstract
BackgroundCabbage Fusarium wilt is a major disease worldwide that can cause severe yield loss in cabbage (Brassica olerecea). Although markers linked to the resistance gene FOC1 have been identified, no candidate gene for it has been determined so far. In this study, we report the fine mapping and analysis of a candidate gene for FOC1 using a double haploid (DH) population with 160 lines and a F2 population of 4000 individuals derived from the same parental lines.ResultsWe confirmed that the resistance to Fusarium wilt was controlled by a single dominant gene based on the resistance segregation ratio of the two populations. Using InDel primers designed from whole-genome re-sequencing data for the two parental lines (the resistant inbred-line 99–77 and the highly susceptible line 99–91) and the DH population, we mapped the resistance gene to a 382-kb genomic region on chromosome C06. Using the F2 population, we narrowed the region to an 84-kb interval that harbored ten genes, including four probable resistance genes (R genes): Bol037156, Bol037157, Bol037158 and Bol037161 according to the gene annotations from BRAD, the genomic database for B. oleracea. After correcting the model of the these genes, we re-predicted two R genes in the target region: re-Bol037156 and re-Bol0371578. The latter was excluded after we compared the two genes’ sequences between ten resistant materials and ten susceptible materials. For re-Bol037156, we found high identity among the sequences of the resistant lines, while among the susceptible lines, there were two types of InDels (a 1-bp insertion and a 10-bp deletion), each of which caused a frameshift and terminating mutation in the cDNA sequences. Further sequence analysis of the two InDel loci from 80 lines (40 resistant and 40 susceptible) also showed that all 40 R lines had no InDel mutation while 39 out of 40 S lines matched the two types of loci. Thus re-Bol037156 was identified as a likely candidate gene for FOC1 in cabbage.ConclusionsThis work may lay the foundation for marker-assisted selection as well as for further function analysis of the FOC1 gene.
Highlights
Cabbage Fusarium wilt is a major disease worldwide that can cause severe yield loss in cabbage (Brassica olerecea)
The objectives of the current study were (i) to fine map the FOC1 gene using one double haploid (DH) and one F2 population, and newly developed insertion/ deletion (InDel) markers designed from the whole-genome re-sequencing data of the two parental lines (the resistant inbred-line 99–77 and the highly susceptible line 99–91, and (ii) to analyze the genes that fell into the candidate genomic region, and identify the candidate gene
Resistance segregation of the DH and F2 populations We obtained a total of 160 DH lines through microspore culture [20] and over 4000 F2 individuals derived from the same parental lines through hand pollination
Summary
Cabbage Fusarium wilt is a major disease worldwide that can cause severe yield loss in cabbage (Brassica olerecea). Cabbage Fusarium wilt (CFW) is a destructive fungal disease caused by Fusarium oxysporum f. Conglutinans, which for many years has caused severe losses to cabbage yields all over the world. CFW was discovered in several provinces in China and has spread rapidly [3,4,5]. It is a typical soil-borne disease that is hard to control by traditional methods such as chemicals and crop rotation. The most effective control has been the use of resistant cabbage varieties [6,7,8]. The development and use of new resources have become the main goals in current resistance breeding programs for cabbage
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